Active matrix display device

Abstract: An active matrix display device is disclosed which realizes changing over between a wide display and a normal display with a simple construction. The active matrix display device includes picture elements disposed in rows and columns on a horizontally elongated screen. A gate line is connected to each picture element row while a data line is connected to each picture element column. A signal line for supplying a video signal and data lines are connected by way of sampling switches. A horizontal shift register controls sequential opening and closing operations of the sampling switches. The picture element columns of the horizontally elongated screen are divided into a predetermined area allocated to a normal display and a pair of expansion areas included in a wide display. The horizontal shift register is divided into a predetermined stage section corresponding to the predetermined area and expansion stage sections corresponding to the expansion areas. Upon wide display, the predetermined and expansion stage sections of the horizontal shift register are interconnected serially into an integrated condition, but upon normal display, the expansion stage sections are disconnected from the predetermined stage section.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to an active matrix display device in accordance with the precharacterizing part of claim 1 which can change over between a display of the aspect ratio of 16:9 and another display of the aspect ratio of 4:3. An active matrix display device of that kind is known from PATENT ABSTRACTS OF JAPAN, vol. 14, No. 391, (E-968), JP-A-02143781. 2. Description of the Related Art Development of active matrix display devices conforming to the high definition television standards has been and is performed in recent years. An active matrix display device conforming to the high definition television standards has such a horizontally elongated screen as shown in FIG. 5 and allows a display of the aspect ratio of 16:9 (such display will be hereinafter referred to as wide display). A large number of picture elements PXL are disposed in rows and columns on the screen so as to satisfy the aspect ratio of 16:9. Meanwhile, another active matrix display device having an ordinary screen size performs another display of the aspect ratio of 4:3 (such display will be hereinafter referred to as normal display). In an active matrix display device of the high definition television standards, a structure which allows changing over between a wide display and a normal display is known. In order to perform a wide display with the active matrix display device of the high definition television standards, all picture element columns are used as seen in FIG. 5. On the other hand, in order to effect a normal display, since conversion in aspect ratio to 4:3 is involved, only those of the picture element columns which belong, for example, to a central area B shown in FIG. 5 are used to construct a display screen. In this instance, areas A and C on the opposite sides of the central area B are masked, for example, with side black. Various means have been proposed for a changing over method between a wide display and a normal display. One of such methods involves compression processing of a video signal as illustrated in FIGS. 6(A) and 6(B). When a video signal for a normal display is inputted as seen from the waveform of FIG. 6(A), it is first converted by A/D conversion into digital data. In order to distribute the digital data only to the central area B of the horizontally elongated screen shown in FIG. 5, compression processing for each one horizontal period (lH) is performed at a desired ratio as seen from the waveform of FIG. 6(2). The digital data obtained by the compression processing is distributed to the area B while fixed data for a masked display are supplied to the areas A and C (FIG. 5) on the opposite sides of the area B. However, the present compression processing method has a subject to be solved in that a digital processing circuit to be externally added is large in scale and this makes a factor of increase of the cost. Another structure has been proposed and is known wherein a mechanical shutter is disposed at each of the areas A and C at the opposite ends of the horizontally elongated screen in place of a masked display which is based on electric processing. However, the alternative structure has another subject to be solved in that, since a physical mechanism is required, it is complicated in structure, which makes a cause of failure. PATENT ABSTRACTS OF JAPAN, vol. 14, No. 391, (E-968), JP-A-02143781 describes a known active matrix display device in accordance with the precharacterizing part of claim 1. The switching means S7, S8 for switching the different stages of the combined shift register 34-36 and the switching means S9, S10 for switching the masking means 37-39 in accordance with the different display modes of the known active matrix display device are shown to have common switching positions a, b, c to be switched in combination so that switching over the display modes and the masking operation are not independent from each other. SUMMARY OF THE INVENTION It is an object of the present invention to provide an active matrix display device which allows changing over between a wide display and a normal display with a simple structure that a versatile driving system can operate various displays such as a liquid crystal display, a plasma display and a plasma addressed liquid crystal display and that it is possible to effect desired masked display in the expansion area of the screen even after a video signal is written into the picture element columns. In order to achieve the above object, according to an aspect of the present invention, there is provided an active matrix display device, comprising: a plurality of picture elements disposed in rows and columns on a horizontally elongated screen, the columns of said picture elements being divided into a first area allocated to a normal display and a second area included in a wide display; a gate line connected to each of the rows of said picture elements; a vertical drive circuit connected to the gate lines; a data line connected to each of the columns of said picture elements; a signal line for supplying a video signal; a plurality of sampling switches for interconnecting said signal line and the data lines; and a horizontal shift register for controlling sequential opening and closing operations of said sampling switches, said horizontal shift register being divided into a predetermined first, second and third stage section, wherein the second stage section corresponds to those of the columns of said picture elements in said first area and said first and third stage sections correspond to those of the columns of said picture elements in said second area, and masking means for supplying, upon normal display, a signal of a fixed level to those of the data lines which belong to said second area to mask said second area, characterized in that a first gate circuit is connected to an input terminal of said first stage section and to a second gate circuit which is interposed between an output of said first stage section and an input terminal of said second stage section, a third gate circuit is interposed between an output terminal of said second stage section and an input terminal of said third stage section, said first to third gate circuits including logic means so that said first to third gate circuits can be switchably controlled according to a desired normal display mode or widened display mode by control signals supplied from a common control line, and in that said masking means are individually constituted from transfer gates which are individually connected to each of the data lines of the columns of said display screen, wherein said transfer gates are provided separately from said first to third gate circuits and can be controlled by applying masking control signals separately for said first area and said second area and separately from said control signals applied to said first to third gate circuits, and for a masking process two separate masking signals each having a predetermined level are respectively applied to said data lines of said first area and said second area respectively, and the display of said second area (A, C) can be selected in accordance with a display mode such as normal display mode or widened display mode as a white display, dark display or a desired intermediate color display. In the active matrix display device, the horizontal shift register, which is constituted from a multiple connection of flipflops, is divided into a second or predetermined stage section and the expansion stages forming a first and third stage section. The second stage section corresponds to a normal display while the expansion stage sections namely the first and third stage sections correspond to an expansion area when wide display is performed. The first to third stage sections are interconnected by way of the gate circuits. In a wide display, the second or predetermined stage section and the first and third stage sections are serially connected to each other into an integrated condition by way of the gate circuits, but in a normal display, the first and third stage sections are disconnected from the second or predetermined stage section. In this manner, changing over between a wide display and a normal display can be realized by the simple construction that gate circuits are added to the horizontal shift register of the divisional construction. Accordingly, the active matrix display device is advantageous in terms of the cost since particularly complicated digital processing of a video signal is not required. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference characters. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an active matrix display device showing a preferred embodiment of the present invention; FIG. 2 is a block diagram showing a gate circuit of the active matrix display device shown in FIG. 1; FIG. 3 is a circuit diagram showing masking means of the active matrix display device shown in FIG. 1; FIG. 4 is a waveform diagram showing the waveform of a masking signal; FIG. 5 is a diagrammatic view showing the construction of a screen of an active matrix display device for a wide display; and FIGS. 6( A) and 6( B) are waveform diagrams illustrating a conventional changing over method of a wide display/normal display device. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, there is shown a basic construction of an active matrix display device according to the present invention. The active matrix display device shown includes a plurality of picture elements (PXL) disposed in rows and columns on a horizontally elongated screen. A gate line 1 is connected to each of the rows of the picture element. A vertical driver or vertical drive circuit 2 is connected to the gate lines 1. A data line 3 is connected to each of the columns of the picture elements. A signal line 4 is disposed for supplying a video signal or image signal Vsig to the picture elements. The signal line 4 and the data lines 3 are connected to each other by way of a plurality of sampling switches SW. The sampling switches SW are sequentially operated to open or close under the control of a horizontal shift register (SR) by way of a horizontal driver 5. The picture element columns of the horizontally elongated screen are divided into a predetermined area allocated to a normal display and a pair of expansion areas included in a wide display. In the present embodiment, the predetermined area includes the picture element columns from the L+lth to Mth picture element columns both inclusive while the expansion areas include the picture element columns from the first to Lth picture element columns both inclusive and from the M+lth to Nth picture element columns both inclusive. In the meantime, the horizontal shift register (SR) is divided into three stage sections including a predetermined stage section SRB corresponding to the picture element columns of the predetermined area and a pair of expansion stage sections SRA and SRC corresponding to the picture element columns of the expansion areas. Upon wide display, the predetermined stage section SRB and the expansion stage sections SRA and SRC of the horizontal shift register are serially connected into an integrated condition and sequentially operate the sampling switches SW to open or close. Upon normal display, the expansion stage sections SRA and SRB of the horizontal shift register (SR) are disconnected from the predetermined stage section SRB and only those of the sampling switches SW which belong to the predetermined area are sequentially operated to open or close. Again, in the present embodiment, the horizontal shift register is divided into three portions including the expansion front stage section SRA, the predetermined middle stage section SRB, and the expansion rear stage section SRC. A first gate circuit G0 is connected to an input terminal of the expansion front stage section SRA. A second gate circuit G1 is interposed between an output terminal of the expansion front stage section SRA and an input terminal of the predetermined middle stage section SRB. A third gate circuit G2 is interposed between an output terminal of the predetermined middle stage section SRB and an input terminal of the expansion rear stage section SRC. The gate circuits G0, G1 and G2 are controlled to be switched by control signals CTL0, CTL1 and CTL2, respectively, to selectively perform connection integration and disconnection of the horizontal shift register. A start signal ST for the shift register is supplied to the first gate circuit G0 at the top of the three gate circuits G0, G1 and G2. The active matrix display device further includes masking means, and upon normal display, a signal (masking signal) of a fixed level is supplied to those of the data lines 3 which belong to the expansion areas to selectively effect masked display of the expansion areas (side black display). In the present embodiment, the masking means is constituted from a plurality of gate elements GA which belong to one of the expansion areas, another plurality of gate elements GB which belong to the central predetermined area, and a further plurality of gate elements GC which belong to the other expansion area. The gate elements GA are individually connected to those of the gate lines 3 which correspond to the first to Lth picture element columns. The gate elements GB are individually connected to those of the gate lines 3 which correspond to the L+lth to Mth picture element columns. The gate elements GC are connected to those of the gate lines 3 which corresponds to the M+lth to Nth picture element columns. The gate elements GA and GC receive a masking signal MSKA, and the gate electrodes GB receives another masking signal MSKB. The gate elements GA and GC are controlled to be opened or closed by a control signal CTLA, and the gate elements GB are controlled to be opened or closed by another control signal CTLB. Subsequently, operation of the active matrix display device shown in FIG. 1 will be described in detail with reference to FIGS. 2 to 4. FIG. 2 shows a detailed circuit construction of the gate circuits GO, G1 and G2. Referring first to FIG. 2, the first gate circuit GO is constituted from a pair of AND elements AND1 and AND2. The second gate circuit Gl is constituted from a pair of AND elements AND3 and AND4 and a single OR circuit OR1. The third gate circuit G2 is constituted from a single AND element ANDS. In the construction, when wide display is effected, all of the control signals CTL0, CTL1 and CTL2 are set to a low level by an external control circuit. It is to be noted that, in some cases, the control signals CTL0, CTL1 and CTL2 may be supplied from a common control line. Upon wide display, when the control signal CTL0 is set to a low level, the AND element AND1 is closed while the AND element AND2 is opened. As a result, a start signal ST inputted to the first gate circuit G0 is supplied to the expansion front stage section SRA of the horizontal shift register by way of the AND element AND2. The expansion front stage section SRA sequentially transfers the start signal ST in synchronism with a predetermined clock signal to sequentially open the sampling switches SW corresponding to the first column to the Lth column by way of the horizontal driver 5 (FIG. 1). As a result, a video signal Vsig supplied from the signal line 4 is sampled to those of the data lines 3 which correspond to the picture element columns from the first column to the Lth column. Subsequently, at the second gate circuit G1, the AND element AND3 is in a closed condition while the AND element AND4 is in an open condition. Consequently, an output signal of the expansion front stage section SRA is supplied to an input terminal of the predetermined middle stage section SRB by way of the AND element AND4 and the OR circuit OR1. Also the predetermined middle stage section SRB sequentially performs signal transfer in a similar manner as described above to control and drive the corresponding L+lth to Mth picture element columns. Finally, since the control signal CTL2 is at a low level, the AND element AND5 of the third gate circuit G2 is in an open state. Accordingly, an output signal of the predetermined middle stage section SRB passes the AND element AND5 and is inputted to the expansion rear stage section SRC. The expansion rear stage section SRC performs signal transfer in a similar manner as described above to control and sequentially drive the corresponding M+lth to Nth picture element columns. As a result of the operation described above, all of the first to Nth picture element columns are sequentially driven to effect wide display. On the other hand, upon normal display, the control signals CTL0, CTL1 and CTL2 are set to a high level. In this instance, the AND element AND1 of the first gate circuit G0 is opened, and AND element AND2 is closed. Accordingly, a start signal ST inputted to the first gate circuit G0 is inputted to the second gate circuit G1 through the AND element AND1. Consequently, the expansion front stage section SRA of the horizontal shift register is put into a disconnected condition. When the control signal CTL1 is at a high level, the AND element AND3 of the second gate circuit G1 is opened and the AND element AND4 is closed. Consequently, the start signal ST passes the AND element AND3 and the OR circuit OR1 and is supplied to the input terminal of the predetermined middle stage section SRB. The predetermined middle stage section SRB sequentially transfers the start signal ST to drive the corresponding L+lth to Mth picture element columns by way of the horizontal driver 5 and the corresponding switching elements SW. Finally, when the control signal CTL2 is at a high level, the AND element AND5 of the third gate circuit G2 is in a closed condition. Consequently, an output signal of the predetermined middle stage section SRB cannot pass the third gate circuit G2. Consequently, the expansion rear stage section SRC is put into a disconnected condition. Due to the operations described above, upon normal display, only the predetermined middle stage section SRB effects a signal transfer operation. FIG. 3 is a circuit diagram showing a detailed construction example of the masking means described above. Referring to FIG. 3, a picture element array 10 constituting the horizontally elongated screen is divided into a predetermined area 11B allocated to a normal display and a pair of expansion areas 12A and 12B included in a wide display. The first to Lth picture element columns belong to the expansion area 12A; the L+lth to Mth picture element columns belong to the central predetermined area 11B; and the M+lth to Nth picture element columns are included in the other expansion area 11C. The gate elements GA disposed for the expansion area 12A are individually constituted from transmission gates and connected to the corresponding data lines 3. Similarly, also the gate elements GB disposed in the predetermined area 11B are formed from transmission gates and individually connected to the corresponding data lines 3. Also the gate elements GC disposed in the expansion area 12C are formed from transmission gates and individually connected to the corresponding data lines 3. A predetermined masking signal MSKA is supplied to the gate elements GA and GC which belong to the expansion areas 12A and 12C while another masking signal MSKB is supplied to the gate elements GB which belong to the predetermined area 11B. Further, a control signal CTLA and another control signal CTLA , which is an inverted signal of the control signal CTLA and accordingly is indicated by CTLA with an upper horizontal bar applied thereto, are applied to control terminals of the transmission gate elements GA and GC. Another pair of control signals CTLBL and CTLBH are supplied to control terminals of the transmission gate elements GB. With the masking means having the construction described above, upon normal display, the control signal CTLA is set to a high level so that the gate elements GA and GC are put into an open state. Consequently, the masking signal MSKA having a predetermined level is distributed to the expansion areas 12A and 12C by way of the gate elements GA and GC, respectively, so that a desired masked display is provided. On the other hand, upon wide display, the control signal CTLA is changed over to a low level so that the gate elements 12A and 12C are put into a closed state. Consequently, the masking signal MSKA is not supplied to the expansion areas 12A and 12C. Meanwhile, since a video signal is supplied to the entire picture element array 10 by way of the sampling switches SW (FIG. 1) as described hereinabove, desired masked display is performed. Meanwhile, the control signal CTLBL is always set to a low level while the control signal CTLBH is always set to a high level. Consequently, in any of a wide display and a normal display, the gate elements GB which belong to the predetermined area 11B remain in a disconnected condition. Consequently, the masking signal MSKB is not supplied to the predetermined area 11B at all. In this manner, since the gate elements GB remain in a normally off state, they need not necessarily be incorporated in the circuit. However, actually it is preferable to add the gate elements GB having an equal size as dummy gates to those of the gate elements GA and GC in order to make the loads to all of the data lines 3 equal among them. Since the gate elements GB are normally off, the masking signal MSKB may be set to any level in principle. Actually, it is preferable to set it to a level at which the leak current of the gate elements GB exhibits a minimum level. The active matrix display device according to the present invention includes various displays such as, for example, a liquid crystal displays, a plasma display, and a plasma addressed liquid crystal display. In a liquid crystal display, each picture element is constituted from a picture element electrode, a thin film transistor and so forth. The gate electrode of the thin film transistor is connected to a corresponding gate line; the source electrode is connected to a corresponding data line; and the drain electrode is connected to a corresponding picture element electrode. A substrate on which an array of such picture elements is formed is adhered to an opposing substrate, on which opposing electrodes are formed, with a predetermined gap left therebetween, and liquid crystal is filled and enclosed in the gap thereby to make up an active matrix liquid crystal display device. On the other hand, in a liquid crystal display device, ac reversal driving is normally performed. The ac reversal driving involves 1H reversal corresponding to a horizontal synchronizing signal and 1F reversal corresponding to a vertical synchronizing signal. In the waveform diagram of FIG. 4, the video signal Vsig is reversed by 1H reversal, and the polarity thereof is reversed with reference to a predetermined reference potential Vref for each horizontal period. In this instance, also the masking signal MSKA is a square wave which exhibits reversal in polarity for each horizontal period. Consequently, where the liquid crystal display is in a normally white mode, the expansion areas provide a dark display, and accordingly, so-called side black processing can be performed. However, in the present invention, the display of the expansion areas in a normal display is not limited to a black display, but may be a white display or a desired intermediate color display. It is to be noted that, as regards the other masking signal MSKB, a fixed signal, for example, of a level equal to the reference potential Vref may be supplied so that the leak current of the normally off gate elements GB may be suppressed as described hereinabove. It is to be noted that, while, in the embodiment described above, the relationship of the numbers of stages and the positions of the stage sections and the gate elements SRA and GA, SRB and GB, and SRC and GC is selected to 1:1, the relationship of them is not limited to this particular one. Further, even after a video signal is written into the picture element columns by way of the sampling switches SW, it is possible to effect desired masked display in the expansion areas by writing a side masking signal by way of the gate elements GA and GC.

Claims: An active matrix display device, comprising: a plurality of picture elements (PxL) disposed in rows and columns on a horizontally elongated screen, the columns of said picture elements being divided into a first area (B) allocated to a normal display and a second area (A, C) included in a wide display; a gate line (1) connected to each of the rows of said picture elements; a vertical drive circuit (2) connected to the gate lines (1); a data line (3) connected to each of the columns (1-L, L+1-M, M+1 N) of said picture elements (PxL); a signal line (4) for supplying a video signal (Vsig); a plurality of sampling switches (SW) for interconnecting said signal line (4) and the data lines (3); and a horizontal shift register (SRA, SRB, SRC) for controlling sequential opening and closing operations of said sampling switches (SW), said horizontal shift register being divided into a predetermined first, second and third stage section (SRA, SRB, SRC), wherein the second stage section corresponds to those of the columns of said picture elements in said first area (B) and said first and third stage sections (SRA, SRC) correspond to those of the columns of said picture elements in said second area (A, C), and masking means for supplying, upon normal display, a signal of a fixed level to those of the data lines which belong to said second area to mask said second area, characterized in that a first gate circuit (G0) is connected to an input terminal of said first stage section (SRA) and to a second gate circuit (G1) which is interposed between an output of said first stage section (SRA) and an input terminal of said second stage section (SRB), a third gate circuit (G2) is interposed between an output terminal of said second stage section (SRB) and an input terminal of said third stage section (SRC), said first to third gate circuits (G0-G2) including logic means (AND1 to ANDS, OR1) so that said first to third gate circuits (G0-G2) can be switchably controlled according to a desired normal display mode or widened display mode by control signals (CTL0, CTL1, CTL2) supplied from a common control line, and in that said masking means are individually constituted from transfer gates (GA, GB, GC) which are individually connected to each of the data lines (3) of the columns of said display screen, wherein said transfer gates (GA, GB, GC) are provided separately from said first to third gate circuits and can be controlled by applying masking control signals (CTLA, CTLA , CTLBL, CTLBH) separately for said first area (B) and said second area (A, C) and separately from said control signals (CTL0, CTL1, CTL2) applied to said first to third gate circuits (G0-G2), and for a masking process two separate masking signals (MSKA, MSKB) each having a predetermined level are respectively applied to said data lines (3) of said first area (B) and said second area (A, C) respectively, and the display of said second area (A, C) can be selected in accordance with a display mode such as normal display mode or widened display mode as a white display, dark display or a desired intermediate color display.

Inventors: MAEKAWA TOSHIKAZU, MAEKAWA, TOSHIKAZU
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: H04N3
IPC codes: G09G3, H04N3, H04N5